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Bubble Induced Mixing In A Bubble Column With Counter-Current Liquid Flow

Péter Kováts, Katharina Zähringer

Otto-von-Guericke-Universität Magdeburg, Magdeburg, Germany


Bubble columns have been widely investigated over the last few decades, concentrating on the bubble parameters, and gas/liquid motion. However, mixing and often the resulting interaction between chemical reaction and hydrodynamics in the column are rarely analysed. For this reason, experiments with Laser Induced Fluorescence (LIF) applying Sulforhodamine G as fluorescent dye, and shadow imaging were performed in a square laboratory-scale counter-current flow bubble column at 21 different flow conditions and three different dye inlet positions. In these experiments the mixing efficiency was investigated by varying the bubble size, the gas and the liquid flow rates, to obtain the necessary data for a further understanding of mixing processes in bubbly flows. The strong influence of the bubble presence, their size and the counter-current liquid flow rate on mixing in the column is obvious from these results. Bubble induced mixing leads to a good homogenisation inside the column, compared to a flow without bubbles. Also, the larger the bubbles the higher the bubble induced upward velocity, which leads to a better mixing. The highest counter-current liquid flow rate led to a more concentrated dye jet, which was less dispersed than at lower liquid flow rates, while the moderate counter-current liquid flow rate (11.1 l· min-1) has been found optimal for mixing in the investigated cases. The combination of large bubbles generated with the 3.6 mm capillaries, and a moderate counter-current liquid flow rate led to the best mixing performance in the bubble column.

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